Low friction piston for gas flow calibration systems

Abstract

A calibration system for a tube prover used in gas flow rate calibration equipment includes a low friction piston which provides an effective seal without the use of mercury. The low friction piston is easily movable in a prover tube of the calibration system in response to gas flow rates, even low flow rates. The piston is constructed of a light weight, low friction fluorinated hydrocarbon material. The piston has first and second seals which provide a positive seal with the inner surface of the prover tube and which maintain the alignment of the piston within the prover tube.

I claim:  
     
       1. A low friction piston for sealing an inner surface of a gas flow calibration system comprising: 
       a piston body being movable longitudinally in the calibration tube in response to a gas flow in the calibration system, the piston body being formed of a resilient material;  
       a first sealing skirt extending from a portion of the piston body to contact the inner surface of the calibration tube and seal against leakage of the gas flow past the piston body in the calibration tube; and  
       a second sealing skirt integrally formed with and extending from a portion of the piston body to contact the inner surface of the calibration tube, the second sealing skirt having passages adapted to allow the gas flow to pass by the second sealing skirt.  
     
     
       2. The low friction piston of  claim 1 , wherein the inner surface of the tube includes an inner diameter and the second sealing skirt has an outer diameter greater than the inner diameter of the tube. 
     
     
       3. The low friction piston of  claim 1 , wherein the resilient material of the piston body is fluorinated hydrocarbon. 
     
     
       4. The low friction piston of  claim 1 , wherein at least one sealing skirt is adapted to be in dry contact with the inner surface of the calibration tube. 
     
     
       5. The low friction piston of  claim 1 , wherein at least one sealing skirt of the piston is adapted to contact the inner surface of the calibration tube with an interference fit. 
     
     
       6. The low friction piston of  claim 1 , wherein the inner surface of the tube has an inner diameter and at least one sealing skirt has an outer diameter greater than the inner diameter of the tube. 
     
     
       7. The low friction piston of  claim 1 , wherein at least one sealing skirt has a first thickness adjacent the piston body and has a second thickness adjacent the inner surface of the calibration tube, and the first thickness is greater than the second thickness. 
     
     
       8. The low friction piston of  claim 1 , wherein the piston body includes a weight reducing cavity formed in an outer end of the piston body. 
     
     
       9. The low friction piston of  claim 1 , wherein the piston body includes a weight reducing cavity formed in an inner end of the piston body. 
     
     
       10. The low friction piston of  claim 1 , wherein the piston body has an outside diameter and at least one reduced diameter portion having a diameter which is less than the outside diameter of the piston body. 
     
     
       11. The low friction piston of  claim 1 , wherein the first sealing skirt is formed integrally with the piston body. 
     
     
       12. The low friction piston of  claim 1 , wherein the resilient material of the piston body is a synthetic resin material. 
     
     
       13. A low friction piston-glass tube prover assembly for use in a gas flow calibration system comprising: 
       a calibration tube having an inner surface;  
       a piston with an outer end and an outside diameter, the piston being disposed within the calibration tube in sealing communication with the inner surface of the calibration tube;  
       a first flexible sealing skirt disposed on the piston in contact with the inner surface of the calibration tube; and  
       a second sealing skirt formed integrally with the piston and contacting the inner surface of the calibration tube, the second sealing skirt having passages adapted to allow the gas flow to pass between the second sealing skirt and the inner surface of the calibration tube.  
     
     
       14. The low friction piston-glass tube prover assembly of  claim 13 , wherein the second sealing skirt has an inner portion connected to the piston, and an outer portion in contact with the inner surface of the tube, and the inner portion is thicker than the outer portion. 
     
     
       15. The low friction piston-glass tube prover assembly of  claim 13 , wherein the inner surface of the calibration tube has an inner diameter, and the second sealing skirt has an outer diameter greater than the inner diameter of the calibration tube. 
     
     
       16. The low friction piston-glass tube prover assembly of  claim 13 , wherein at least one sealing skirt has an inner portion connected to the piston, and an outer portion in contact with the inner surface of the tube, and the inner portion is thicker than the outer portion. 
     
     
       17. The low friction piston-glass tube prover assembly of  claim 13 , wherein at least one sealing skirt of the piston is in dry contact with the inner surface of the calibration tube. 
     
     
       18. The low friction piston-glass tube prover assembly of  claim 13 , wherein at least one of the sealing skirts contacts the inner surface of the calibration tube in an interference fit. 
     
     
       19. The low friction piston-glass tube prover assembly of  claim 13 , wherein the inner surface of the calibration tube has an inner diameter, and the sealing skirt has an outer diameter and the outer diameter of at least one of the sealing skirts is greater than the inner diameter of the calibration tube. 
     
     
       20. A tube prover flow calibration system comprising: 
       at least one calibration tube, having an inner surface and an inner diameter;  
       at least one piston having an outer end, an inner end and an outside diameter disposed within the at least one calibration tube in sealing communication with the inner surface of the cylindrical tube;  
       at least one flexible sealing skirt located toward the outer end of the at least one piston for maintaining continuous contact with the inner surface of the tube;  
       a second sealing skirt formed integrally with the piston and contacting the inner surface of the calibration tube, the second sealing skirt having passages adapted to allow the gas flow to pass between the second sealing skirt and the inner surface of the calibration tube; and  
       a processor for computing gas flow rate based upon sensed movement of the piston within the tube.  
     
     
       21. The calibration system of  claim 20 , wherein the second sealing skirt has an inner portion connected to the piston, and an outer portion in contact with the inner surface of the tube, and the inner portion is thicker than the outer portion. 
     
     
       22. The calibration system of  claim 20 , wherein the inner surface of the calibration tube has an inner diameter, and the second sealing skirt has an outer diameter greater than the inner diameter of the calibration tube. 
     
     
       23. The calibration system of  claim 20 , wherein at least one sealing skirt has an inner portion connected to the piston, and an outer portion in contact with the inner surface of the tube, and the inner portion is thicker than the outer portion. 
     
     
       24. The calibration system of  claim 20 , wherein at least one sealing skirt of the piston is in dry contact with the inner surface of the calibration tube. 
     
     
       25. The calibration system of  claim 20 , wherein at least one of the sealing skirts contacts the inner surface of the calibration tube in an interference fit. 
     
     
       26. The calibration system of  claim 20 , wherein the inner surface of the calibration tube has an inner diameter, and the sealing skirt has an outer diameter greater than the inner diameter of the calibration tube. 
     
     
       27. A low friction piston for sealing an inner surface of a gas flow calibration tube in a flow calibration system comprising: 
       a piston body being movable longitudinally in the calibration tube in response to a gas flow in the calibration system, the piston body being formed of a material;  
       a first sealing skirt extending outwardly from a portion of the piston body to contact the inner surface of the calibration tube and seal against leakage of the gas flow past the piston body in the calibration tube; and  
       a second sealing skirt integrally formed with and extending outwardly from a portion of the piston body in a corresponding direction to the first sealing skirt to contact the inner surface of the calibration tube to provide proper alignment of the piston body in the calibration.